While the wolf is away: Modelling the dynamics of a moose population in a protected area

Populations at high density can threaten the ecological integrity of
ecosystems through cascading effects. When such situations arise,
management practices must be guided by sufficient knowledge of the
biological mechanisms at play. Simulation models are powerful tools for
acquiring such knowledge. The moose (Alces alces americana) is a species
that recently became overabundant in some areas of eastern North America,
sometimes requiring specific management measures. While numerous models
exist for moose population dynamics, few of them are adapted to high
density populations like the one in Forillon National Park (Quebec,
Canada), a protected area in which the moose's apical predator (grey
wolf Canis lupus) is absent. We developed a sex- and age-structured
population model respecting these conditions that we parameterized using
pattern-oriented modelling. The most plausible sequence of vital rates
identified exhibited strong negative density dependence in survival,
reproduction and dispersal. Predation by alternative predators, black
bears (Ursus americanus) and coyotes (Canis latrans), caused substantial
mortality of calves each year. Contrary to other areas in northeastern
North America, winter tick only had a slight effect on calf survival,
except when moose density approached carrying capacity. The variations in
the population’s sex ratio were mainly explained by a sex-biased
dispersal. Our study provides new insights concerning the dynamics of
high-density ungulate populations in the absence of their apical predator,
and our modelling approach helped to shed light on new methodological
challenges and opportunities. We also present a comprehensive process to
build a complex population model and parameterize it while using scarce
data.